1. Technical Field
The present invention relates to probe assemblies in general, and in particular to a probing assembly for testing integrated circuits fabricated on a wafer.
2. Description of Related Art
After integrated circuits (ICs) have been fabricated on a wafer, the wafer can be divided into multiple rectangular-shaped chips. Each chip has a rectangular (or other regular) arrangement of metallic contact pads through which electrical connections can be made. For efficiency sake, the testing of the chips is preferably performed while the chips are still joined together on the wafer. One typical procedure is to support the wafer on a flat stage or “chuck” and to move the wafer in X, Y and Z directions relative to the head of a probing assembly so that contacts on the probing assembly move relative to the surface of the wafer for consecutive engagement with the bond pads of one or more of test structures on the wafer. Various conductors that interconnect the test instrumentation with the contacts on the probing system enable each chip on the wafer to be sequentially connected to the test instrumentation and be tested.
The contacts of a conventional probing system include a beam affixed to the lower surface of a membrane assembly and is conductively interconnected with corresponding traces located on the surface of a membrane of the membrane assembly. A contact bump for engaging a bond pad of a device-under-test (DUT) is affixed to one end of the beam. When the contact bump is pressed against the bond pad of the DUT, the membrane assembly is deflected, compressing a portion of the elastomeric layer proximate the end of the beam to which the contact bump is affixed. The compliance of the elastomeric layer enables relative displacement of the respective contact bumps and facilitates simultaneous engagement with multiple bond pads that may have respective contact surfaces that lie in different planes. The resilience of an elastomeric layer of the membrane assembly controls the force exerted by the contacts and returns the contacts to the at-rest position when the probe is withdrawn from pressing engagement with the DUT. In order to maintain good compliance, more forces need to be exerted on the membrane assembly, which can shortened the service life of the membrane assembly.
Consequently, it would be desirable to provide an improved probing assembly.